1. Field of the Invention
The present invention relates generally to optical instruments and, more particularly, to optical instruments employing a truncated prism having its distal surface disposed proximate a planar end of an opaque tubular housing for use in permitting a viewer to observe the physical appearance of an internal wall of an aperture in a printed circuit board.
2. Description of the Prior Art
Heretofore, a device for scanning the internal wall of a hole in a printed circuit board or the like in order to determine if there are blemishes has not been available. Such blemishes, for example, can be caused as a result of a void in plating, an improper solder flow or a drilling operation that develops rough spots and burrs and typically have been found to lead to the production of printed circuit boards that have poor electrical connections. As a consequence, inspectors of printed circuit boards have been required to utilize a relatively expensive fisheye-type microscope to detect such blemishes. A disadvantage of such a detection technique is that it is a laborious, time consuming procedure which requires an experienced operator. Furthermore, since only a small portion of the wall is capable of being viewed with a single set up of the microscope, several set-ups are required to observe substantially the entire internal wall of such hole.
An example of a prior art optical instrument for examining an object located in direct or immediate contact with its distal face is found in U.S. Pat. No. 3,357,433, "Endoscope for Illumination and Observation of Contacting Distal Regions," by Max Foursetier, G. F. Guiot, Jacques F. Rougerie, H. N. Vulmiere, and Jacques C. Vulmiere. Although the patent reveals a contact endoscope employing a cylindrically-shaped rod terminating in a member having the shape of a prism, an ogive, etc., it does not reveal an optical instrument employing a truncated prism having its distal end disposed proximate a planar end of an opaque tubular housing which is particularly formed to permit the viewer to observe the physical appearance of the internal wall of an aperture in a printed circuit board.